Although attitudes have changed through the years, the two-child family has largely endured as an American ideal. Now British researchers have discovered a health benefit to having two children.

People who have two children, researchers found, have a significantly lower risk of developing heart disease than those with larger families -- or smaller families with one child or none.

The researchers studied more than 8,000 elderly men and women and found that the more children they had, the more likely they were to have coronary heart disease. Among women, the risk increased 30% with each child after the second one. For men, the risk increased 12% for each additional child.

People with large families tend to be poorer and have less healthy lifestyles, which explains a large part of the increased risk. In this study, having more children was associated with greater levels of obesity for both men and women. But women who give birth to several children experience other biological changes that affect their risk as well.

In normal pregnancy, women become temporarily insulin-resistant, which is important for normal growth of the baby. With more pregnancies, however, this can result in permanently raised blood sugar, which may cause diabetes, and lower levels of the good, HDL cholesterol -- all increase heart disease risk.

The study also found that having no children or only one increases risk, too. That's probably no longer a factor today when people may choose to be childless. Generations ago, having one or no children was more likely a result of infertility and, says lead researcher Debbie A. Lawlor of the University of Bristol in Britain, there are hormonal conditions that contribute to infertility that also increase heart disease risk later in life.

The study was published in Circulation: Journal of the American Heart Assn.

Monounsaturated fats and vitamin A alleviate different skin problems

There has been a lot of speculation about how various nutrients affect the skin, but little hard evidence. Now Dutch researchers have found that at least two nutrients -- vitamin A and monounsaturated fats -- have an effect on several measures of skin health.

In a study of 300 people, Dutch researchers found that as the amount of vitamin A in the blood increases, sebum, an oily substance produced in the sebaceous glands, decreases. That's helpful for people with oily and/or acne-prone skin. The skin pH also decreased with increasing vitamin A levels, becoming slightly more acidic. That makes skin less hospitable to bacteria, said Dr. Michael F. Holick, a professor at Boston University Medical Center.

People who ate more monounsaturated fats, such as olive oil, had a slight improvement in measures of skin hydration, which helps keep skin soft and smooth. The study was published in the February issue of the American Journal of Clinical Nutrition.

A link between melatonin and contractions

Understanding how melatonin, the sleep hormone, regulates many of the body's cycles one day may lead to new drugs to correct off-kilter rhythms, such as those that cause premature contractions of childbirth.

An American researcher working at the University of Hamburg Medical School in Germany has discovered receptors for melatonin on the muscle cells of the womb or uterus. It's been known that there's a 24-hour rhythm to contractions of the muscles of the womb or uterus, and some speculate that the peak in melatonin that occurs at night explains why more babies are born at night.

Using genetic engineering techniques on muscle cells grown in the lab to identify the receptors, James Olcese and his colleagues found that when receptors from a non-pregnant uterus attached to molecules of melatonin, less cyclic AMP was produced, which sends a chemical signal to the cell telling it to relax. This shows that melatonin is part of the mechanism that controls contractions, said Olcese, a professor at Hamburg's Institute for Hormone and Fertility Research.

The next step is to learn how much melatonin circulating in the blood is enough to activate the receptors, and then observe what the cells do.

The study was published in the February issue of the Journal of Clinical Endocrinology & Metabolism.